Expanded Poly (tetrafluoroethylene) (ePTFE) membranes were modified by graft copolymerization with methacryloxyethyl phosphate (MOEP) in methanol and 2-butanone (also known as methyl ethyl ketone MEK) at ambient temperature using gamma irradiation. The effect of dose rate (0.46 and 4.6 kGy/h), monomer concentration (1-40%) and solvent were studied and the modified membranes were characterised by weight increase, X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XPS was used to determine the % degree of surface coverage using the C-F (ePTFE membrane) and the C-C (MOEP graft-copolymer) peaks. Grafting yield as well as surface coverage were found to increase with increasing monomer concentration and were significantly higher for samples grafted in MEK than in methanol solution. SEM images showed distinctly different surface morphologies for the membranes grafted in methanol (smooth) and MEK (globular) indicating phase separation of the homopolymer in MEK. We propose that in our system, the non-solvent properties of MEK for the homopolymer play a more important role than solvent chain transfer reactions in determining grafting outcomes
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